This invention relates to a method and apparatus for forming a pocketed coil spring mattress having a plurality of rows of closed interconnected fabric pockets, the pockets in each row individually encasing a respective spring, the rows being connected to other such rows by a reinforcing and/or adhesive material, and more particularly to a method and apparatus for positioning, holding and bonding the rows of pocketed coil springs to one another.
It is known to place rows of pocketed coil springs in a parallel fashion to create a mattress, inner spring unit or other body support foundation. A known method for making the rows of encased coil springs is to fold the encasing or pocketing material such that there is a crease on one longitudinal side and an opening on the opposite side. Compressed coils are inserted through the opening between the layers of pocketing material and the opening is sealed by a sealing system, such as a thermal sealing system or stitching. The layers of pocketing material are further sealed between each coil. The coils are than turned and expanded such that one end of the coil is facing the crease of the pocketing material and the other end is facing the sealed opening.
The number of coils in a row and the number of rows are dependent upon the coil spring diameter and the desired finished size of the mattress or the like. The construction of the mattress core may be a plurality of rows of parallel coils with the coils aligned in columns so that the coils line up in both longitudinal and lateral directions, or they may be nested in a honeycomb configuration wherein coils in one row are off-set from coils in the adjacent row.
It is known to connect the rows of coils in a coil to coil manner illustrated in Stumpf U.S. Pat. Nos. 4,566,926 and 4,578,834, and Suenens et al. U.S. Pat. Nos. 5,016,305 and 5,637,178, each of which are hereby incorporated by reference. Nested constructions where rows of coils are interlocked are illustrated in Stumpf U.S. Pat. No. 5,319,815 and German 4,040,220, each of which are hereby incorporated by reference. Other methods of connecting the rows of coils utilize metal clips known as hog rings or they may be stitched with twine which penetrates each row of coils.
Another method in the prior art is the use of rows of coils positioned in a frame with a web of nonwoven material sprayed on the top and bottom of the pocketed coil units, the spray nozzles being manually controlled. Alternatively, or in addition, to the spraying method, beads of hot melt adhesive may be dispensed onto the top and bottom surfaces of the rows of coils and a sheet of nonwoven material pressed against the adhesive containing surfaces.
In Breckle U.S. Pat. No. 4,907,309, a mattress is disclosed having rows of closed fabric pockets with a coil spring positioned in each pocket, there being a plurality of pockets in each row and the rows being connected transversely relative to the direction of the rows by an elastic connecting wall adhesively bonded between each pair of rows. However, the method for forming the mattress is merely disclosed as applying adhesive to an endless strip of connecting wall and pressing an endless row of pockets onto the strip until the connection is made and hardening has occurred. The combination row is then divided transversely into rows of finite length and each such row is thereafter bonded to other rows.
In Suenens et al. U.S. Pat. No. 5,126,004, which does not utilize a connecting wall between the rows of springs, each row of springs is compressed by a pressure plate to hold and position them so that an adhesively coated row may be pushed against another such row. The use of such a pressure plate causes the pocket material to sag and results in a bulging in the center portion of the springs, which was pointed out earlier by Breckle as being a problem.
A similar pocketed coil spring mattress is disclosed in Long et al. U.S. Pat. No. 5,127,635 but the springs in the pockets in each row are formed from a continuous length of wire so that adjacent springs are interconnected, albeit each pocket contains one to three springs. None of this known prior art, however, is directed toward a method and apparatus for manufacturing a pocketed coil spring mattress consistently of a uniform size and in an efficient and practical manner.
In the prior art processes, control and distribution of the adhesive is difficult and inefficient. Some areas of the row may receive too much adhesive while other areas may not receive a sufficient amount of adhesive. Excess adhesive of course is economically inefficient, while risk of separation of the rows of pocketed coil springs from the nonwoven material may result from too little adhesive. Moreover, when adhesive is sprayed there is a tendency for the spray nozzles to clog so that the flow of glue is obstructed. This results in a time consuming cleaning and maintenance program. Additionally, hot melt spraying requires the system to be heated about one hour before spraying can begin. Other difficulties presented by hot melt spraying and application of beads is that the hoses through which the hot melt flows must be insulated to maintain the temperature of the glue within the hose, thereby resulting in very heavy hoses. Since the spraying process involves manually moving the spray nozzle to which the hose is attached to spray the adhesive, the heavy hoses result in the process being slow and fatiguing to the operators who often encounter minor bums from the glue and the nozzles.
Potential solutions for the above-described disadvantages with respect to the adhesive spraying are disclosed in this inventor's pending U.S. patent application Ser. No. 09/024,536, filed Feb. 17, 1998, and U.S. Provisional Patent Application Ser. No. 60/094,135, filed Jul. 24, 1998, each of which are hereby incorporated by reference in their entirety. In one of those methods, the plurality of rows of pocketed coil springs are placed between top and bottom sheets of nonwoven webs of material, each web having a heat activated reinforcement netting. Thus, the rows are attached at their upper and lower surfaces to the sheets of material, rather than on their side surfaces to an adjacent row. In the other method, the nonwoven web of material with reinforcement is positioned between adjacent rows.
A further problem that exists in some of these prior art processes is wear of the pocketing material at the points at which the coils in adjacent rows rub together. Over time, a hole is worn in the pocketing material, resulting in the metal coils rubbing together. The metal on metal rubbing creates undesirable noise when the mattress is in use. Breckel U.S. Pat. No. 4,907,309, as stated previously, provides a connecting wall made of elastic material between the rows of pocketed coil springs, with the wall being adhesively bonded to the rows. Although this reduces wear of the encasing material, an adhesive must still be manually applied to attach the rows to each other and the elastic material adds complexity and cost to the system and potentially reduces the firmness of the spring assembly.